Vitamin D
Vitamin D refers to a group of related fat-soluble vitamins and has many functions in our bodies including aiding:
- Bone mineralisation
- Muscle function
- Nerve conduction
- Regulation of cell growth.
Vitamin D occurs in two forms. Vitamin D3 (cholecalciferol) is produced by the action of ultraviolet light on the skin and Vitamin D2 (ergocalciferol) is produced by plants and can be found in some foods. Vitamin D is not a vitamin in the strict sense and is often considered a hormone because the body can make its own vitamin D from sunlight but your body cannot make other vitamins.
Vitamin D plays an important role in making sure your body and blood have the right amount of calcium, thereby promoting healthy bone formation. It also regulates a number of other important processes in the body, such as activation of both the innate and adaptive immune systems.
Vitamin D it is most effectively synthesized in the skin by the action of UV-B rays in sunlight acting on 7-dehydroxycholesterol. Neither D2 nor D3 — the molecules present in supplements or food — are biologically active forms of the vitamin. The diagram at right shows how vitamin D must first be converted by hydroxylation to calcidiol (usually designated as 25 (OH) D, or just “25-D”) in the liver and then further hydroxylated to calcitriol (1,25 (OH)2 D or just “1,25-D”) in the kidney. It is the 1,25-D form that is biologically active in activating a cascade of important biological functions, such as calcium absorption in the intestines.
Depending on how much calcium you have in your blood, glands called the parathyroid will tell your kidney to either produce or not to produce more 1,25-D. When you do produce more 1,25-D, this helps you absorb more calcium in your gut from your diet. 1,25-D and your parathyroid glands also work together to pull calcium from your bones if needed.
Vitamin D is important for bone health because it ensures your body has all the vitamin D it needs to produce 1,25-D if need be. Without enough vitamin D, your body might not produce as much 1,25-D and have a more difficult time absorbing calcium from your diet. Without getting adequate calcium in your diet and being able to adequately absorb it, you can’t have good bone health.
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